In the case of a large number of industrial processes, a gas, a gas mixture or a liquid flows through a pipeline. In order to be able to control and/or monitor the process, it is, among other things, necessary to know the flow velocity or the mass flow of the medium. A large number of different measuring principles and measuring devices for this purpose are known from the state of the art.
For small flow velocities, thermal flow sensors are frequently used. In a first variant, these comprise: a heating element for warming the medium flowing past, wherein this heating element is operated with constant heating power; and also two temperature sensors; wherein, in each case, one temperature sensor is arranged downstream from the heating element and one upstream from the heating element, and temperatures of the medium are registered. From the temperature difference determined with the two temperature sensors, the flow velocity can be ascertained. So called thermal anemometers are also known. In such case, a heating element is controlled to a constant temperature. The faster the medium flows past the heating element and, in such case, removes heat, the greater the heating power required for keeping the heating element at a constant temperature.
A disadvantage in the case of thermal flow sensors is that they are sensitive to accretions, which may form on them, and, as their lifetime increases, they exhibit a thermal drift. This necessitates frequent maintenance and/or renewed calibration.
Measuring devices based on the Coriolis principle are very reliable. These are essentially composed of at least one oscillatable pipe, which is inserted into a pipeline as an intermediate piece and, on the basis of the Coriolis effect, determines the flow velocity of the medium. Such measuring devices exist in a large number of embodiments and nominal diameters. A disadvantage of Coriolis measuring devices is the high initial investment that they require.